Automatic telephone system



Feb. 10, 1931. J. H. Voss .AUTOMATIC TELEPHONE SYSTEM 3 Sheets-Sheet, 1

Filed Deo.

IRS

0 Hdl Tr-siii?- JmZ-m H. Un s s J. H. VOSS AUTOMATIC TELEPHONE SYSTEM Feb. 10, 1931.

Filed Deo. 24. 1928 3 Sheets-Sheet- 2 Feb. l0, 1931. J. H. Voss 1,792,454

AUTOMATIC TELEPHONE SYSTEM Filed Dec. 24, 1928 3 Sheets-Sheet 3 D UN T0 TEK. KEY a*2 Inusn D1"- Jn'm H. Unss after, reference being had to the accompany-" Patented Feb. 10, 1931 UNITED STATES PATENT OFFICE JOI-IN VOSS, OF BERWYN, ILLINOIS, ASSIGNOR TO RESERVE HOLDING COMPANY, 0F KANSAS CITY, MISSOURI, A CORPORATION 0F DELAWARE AUTOMATIC TIEIILEEHONE SYSTEM Application filed December 24, 1928. `Serial No. 328,089.

The present invention relates to automatic telephone systems in general, but relates more particularly to small systems of this character commonly known as private automatic exchanges. These systems arev as a rule privately owned by individuals or corporations and are installed in factories or'V other establishments for providing local service between a small number of local telephone lines and for establishing connections overtrunk circuits to the main office of thc telephone companys net-work. v

The object of the invention is todp'rovide means whereby a minimum number of switching devices will be employed at the branch exchange for completing lthe desired telephone connections and which will enable the equipment in such exchanges vto be manufactured very cheaply while retaining all of the features necessary for modern high-class and dependable telephone service,

One ofthe features of the invention relates to the improved circuit arrangements of a link circuit comprising a numerical forward selecting switch for connecting with a called line and a non-numerical line finder switch for finding the calling line.`

Another feature relates to the circuit arrangements of animproved trunk finder,-

more than one trunk -finder and which control the trunk finders to com lete the connection to the desiredtlocal subscrlbers line.

Other features, including supervision on trunk calls and night service, are mainly improved circuit'details and will, together with the ones named above, be'explained hereining drawings which comprise Figs. 1 to 3, inclusive, and which show b means of the usual circuit diagrams a suicient amount of apparatus used in systems embodying the features of the invention to enable the invention to be understood.

Fig. l--of the drawings /diagrammatically shows two automatic substations A and A',

together with their individual cut-off relays,

and a common line relay LR which is common to all the subscribers lines, and a finder `connector link circuit. 'The line circuit of each subscribersline terminates in the banks of the finders, such as the finder F, and in the banks o f the connectors, such as the connector .g C. Near the bottom of Fig. 1in the dotted local exchange in the trunk finder TF, thebanks of which are connected in multiple w1th the banks of the connectors, such as C, Fig. 1. Relay 186 near the bottom of Fig.

2 is a. relay which is lcommon tothe trunk finders, such as TF, and which controls the starting leads to theltrunk finders, as will be explained hereinafter. In ordervnot to unduly complicate the drawings onlyvone trunk circuit and one trunk finder has been shown. In case of two or more trunk cir- Vsuits the out start conductor, such as conductor 17 7 would extend through to the second trunk circuit and v,terminate therein in an armature spring similar to armature spring 154. However, as shown in the drawings, the out finder start conductor terminates in a terminal 194 and is jumpered by jumper 195 to terminal 193. Jumper 195 is shown in this manner so as to designate the start circuit extending through two or morev 'trunk circuits and back to terminal l193 which is connected to the common relay 186.

` At CTR in Fig. 3 there is diagrammatically shown the common trunk relays which are common to the trunk finders, such as TF, and which relays are controlled by an attendant .on incommg calls over the vtrunk-circuits,

such as TC, to directively control the operation of the trunk. finders, such as TF, to connect with and ring the desired called line. The'conductors 172, 174, 175, and 176 are common conductors extending to all .of the trunk finders -while the answer control conductor 173 is individual to a. particular trunk soV loo

.swer key AK, and the nightke NI are individnal to the trunk circuit C shown in Fig. 2. Similar answering and supervisory lamps as well as release and answering keys are provided at the attendants cabinet for the other trunk circuits. Relay 207 -is a rey lay common'to all of the keys for controlling the buzzer 222 to signal the attendant. Near the bottom of the figure there is shown a group of conductors which'extend through the keys associated with the second trunk circuit. Terminals 290 and 292 and jumper 291 diagrammatically show how the buzzer connection lead 268 is looped through the various trunk keys to control the circuit of the buzzer 222. At the extreme right of Figf3 there isshown the attendants substation phone which' is of the so-called monophone cradle-type. Theisprings 221 and 222 are shown in normal position with the monophone resting on the cradle. These springs close when the monophone is removed from the cradle. The usual receiver and transmitter as well as the calling device CD A are diagrammatically shown in the usual manner. At LK is shown the line key by means of which the attendant may call or be called in the same manner as a local telephone line. At'2-82 is shown the attendant ringer by means of which the attendant is signaled when called as a local subscriber. The attendants cabinet consists or a flat-top cabineton which is mounted the monophone and the various lam` s and keys.

The automatic rsu stations A and A are similar to each other and each has the usual signaling, talking, and switch-controllin instrumentalities.

similar and each has an individual cut-off relay, such as cut-off relay 4. l

The mechanism of the finders such as F and TF, and the. connectors, such as C, is of the well-known .rotary type, commonly used for rotary line switches, and wipers of which move in a forward direction only and remain. in the position last used. The circuit details of the connector C are Vsomewhat diii'erent fromvthe finders in that a pair of off-normal springs are provided in order tov return the e connector toits normal, or home, positionv after each connection. The trunk finders are also provided Vwith off-normal springs, the` purpose of which is to cause the trunk finders to be returned to their normal positions before-they are directively operated as a connector lto complete a connection to a called line. In Figs. land 2 wherever con?- e The line circuits in w icln the lines of each substation terminate are all?- moans;

ductors terminate in reference characters en' closed in a circle it will be understood that these conductors are to be connected tosimilarly marked conductors.-

In Athe case illustrated, applicant has elected to show a system having a maximum capacity of nine local telephone lines and two trunk lines, although only'one trunk line is shown. The equipment necessary for this exchange would be two iinder connector links, such as shown in Fig. l, and two trunk finders and trunk circuits, such as shown in Fig.

2. With this equipment it is possible to have two local and two trunk connections established at the same time,it being understood that the capacity of the finders and connecters could be readily increased for a larger number of lines if needed. In this case the finders and connectors would probably be call, a circuit is completed for the common line relay LR and the cut-off relay 4Nas follows: from ground through the winding of relay LR, conductor 3, armature 7, through the calling substation loop, armature 5, and through the upper winding of cut-off relay 4 to battery. Cut-oi relay 4 is so adjusted that when the circuit is closed through its upper winding alone, armature 6 is the only armature Awhich is operated.' Cut-ofi relay 4, therefore, may be considered as` a two-step relay in that it operates only its armature 6 on its rst step and its armatures 5 and 7 on =its second step when a circuit is closed for its lower winding. Cut-orf relay 4, therefore, operates its armature 6 in'its first step and prepares a circuit for its lower winding which 1s closed when the nder finds the calling line. Common rline relay LR is operated over the above-traced circuit and closes a c1rcuitl for the finder start relay'l as follows:

ground by Wayf oflarmature 41, armature 36 andits 'resting contact, and winding of finder start'relay '15. to battery. Relay 15, upon izo energizing, at armature 33closes a circuit for -magnet23g Magnet 23 interrupts its own circit and steps the wipers 8, 9, 10, and 11 in Search of the calling line. When wiper 10 engages the bank contacts in whichconductor 88 terminates, said wiper will encounter a battery potential which extends through the lower winding of cut-off relay 4 and the resistance R in parallel for energizing the lower winding of diferential Yrelay 12 and for energizing relaya13. Relay 12, being differentially wound, immediately deenergizes and opens at armature the stepping circuit of magnet 23, thereby stopping the wipers of the finder on the line of the calling subscriber A. Relay 13,\upon energizing, at armature 26 closes a circuit for energizing relay 16. A circuit is also closed from ground at armature 26 for stepping magnet 24 but due to the high resistance 44, vstepping magnet 24 is not operated. Relay 16, upon energizing, at armature 36 opens the start Vcircuit to the slowacting relay 15 at its resting contact, and at its working contact transfers the start lead over conductor 80 to the next Vfinder connector link. The start relay, similar to relay 15 in the next inder connector link, is also a slow-to-energize and slowstorelease 'relay and, therefore, this relay will not completely,

energize to start the next finder because the common line relay LR will .deenergize and open the circuit of this relay before it can operate its armature. At armatures 37 and 38 relay 16 cldses a point in the two talking conductors and also closes a circuit for line relay 17. At armature 39 relay 16 connects ground tovtest wiper 10 which extends `by way of conductor88 and/armature 6 to the energiz'es.

lower winding of cut-off relay 4, thereby com-v pletely energizing the cut-off relay through -its second step to cut off the circuit of the common line relay LRwhich thereupon de- At armature 39 the circuit l through the upper winding of diierential relay 12 is opened and at the working contact of armature 39 the lower winding of dierential relay 12 and the winding of relay 13 are temporarily s'hort-circuited. This short circuit prevents the reenrgization of differential relay 12 and causes relay 13 to deenergize and open the original energizing circuit of relay '16. At armature 40 relay 16 closes a temporary locking circuit for itself extending by way of armature 35. Relay 15, being slow to deenergize aswell .as slow to pull up, maintains its armature 35 in operated posltipn -for a short period of time or long enough to permit line relay 17 and release rela 18 to energize to maintain'relay 16 locke up. .The circuit for energizing line relay 17 may be traced .as follows: ground by Way of the lower winding of relay 17, armature 38, armature 28, line wiper 9, conductor 2, the calling loop at substationV A, conductor 1, line wiper 8, armature 27, arnature 37, and through the upper winding of relay 17 to battery. Line relay 17 upon energizing, at' armature 42 opens 'the normal" short circuit around relay 18 and also closes an energizing circuit for relay 18 as follows:

'places another ground by way of armature 42, winding of release relay 18, armature 68, and win ing of stepping magnet 24 to battery. Stepping magnet 24 does not energize in this circuit on account of the high resistance of relay 18.

VAt armature 43 line relay 17 opens a point in the circuit of slow-acting relay 19. Re- 'lease relay 18,`upon energizing, at armature 45 prepa-res a circuit for switching relay 22; at'armatu-re 46 prepares a circuit for relay 19; at armature 47 also prepares a circuit for relays 19 and locking circuits for relays 20 and 21; at armature 48 prepares another point in the circuit for relay 19; and at armature 49 and its working Contact completes the lookin circuiti for relay 16 before slow-acting re ay 15 has had time to deenergize.

It will be noted-that as soon as relay 16 energizes the calling subscriber receives the dial tone over the following circuit: dial tone lead by way of resting contact of armature 61 andsaid armature; armature 67, condenser c, armature 38, and thence over .the calling loop as previously described. y When the calling subscriber A hears the dial tone he may then dial the number of the desired subscribers line; in this case, since .the desired called subscriber is A', the subscriber will dial the digit 4. Responsive to the operation of the calling device CD at substation A the lcircuit of line relay 17 is interrupted for a plurality of times and .said relay accordingly eenergizes and energizes a correspondingv number of times. Each time line relay 17 deenergizes, a-circuit may be traced for energizing slow acting relay 19 and stepping magnet 24`as follows: ground by way of armature 47, armature S9-and its resting contact,

armature 46, armature 43, through armature 48 to slow-acting relay 19 to battery; another path extends by. way of armature 46 and thence by way of the normally closed springs controlled by armature 42, armature 68, and windingvof stepping magnet 24 to battery. At the normally closed springs controlled by armature 42, relay 18 is short circuited, there,

by rendering said relay slow to release. By

the operation of the stepping magnet 24 the wipers ofthe connector C are rotated steppassing over idle contacts; at armature 52 ound on the impulsing cir-y cuit in case re ay 21`should be energized' while the test wiper 73 is passing oveA grounded contacts. Relay 19, due to its slow to release characteristics,maintains its armatures operated during the impulsing period. Ofi-normal springs 7 O close responsive to the first step of the wipers and provides an additional holding ground for relay 16 as well as preparing a circuit for returning the connector wipers to normal position after con- 5 versation. l i

The further operation now depends upon whether the line of substation A is idle: or busy. In case the line of substation A is busy in another connection, ground will be vpresent i A on the bank' contacts engaged by test wiper 73 and a circuit will be closed for the busy relay 21 as follows: groundv by way of wiper 73, armature 29, armature 51 and its working Contact, resting contact of armature 65 and ,1-5 said armature, and winding of busy relay 2 1 to battery. Relay 2 1, upon energizing at armature 57 opens a point in the circuit of relay at armature 58 opens a point in the circuitv of switching relay 22 ;l at armature 20 59 prepares a, locking circuit for itself which will be closed as soon as slow acting relay 19 deenergizes; and at armature 61' substitutes busy tone for the dial tone whereupon thecalling subscriber A ig given the b usy 25 tone over the circuit previously traced for giving the subscriber the dial tone. A short interval thereafter slow acting relay 19 deenergizes and at the normally closed springs controlled by armature 51 completes the locking circuitl for busy relay 21 as follows: ground by way of armature 47, armature 59 and its working contact, normally closed springs controlled by armature 51, armature 65, and winding of busy relay 21 to battery.

When the calling subscriber hears the well known busy tone he will replace his receiver thereupon opening the circuit of line relay 17. Line relay 17, upon deenergizing, at the normally closed springs controlled by armature 42 places a short circuit around release' relay 18 whereupon the latter relay after an interval releases. Relay 18, upon deenergizing, at larmature 47 opens the locking circuit of busy relay 21 whereupon the latter relay deenergizes. At armature 49 relay 18 coinpletes a circuit for stepping magnet 24 as follows: ground by way ofoffnormal springs 70, armature 49 and its resting Contact, interrupter springs ofstepping magnet 24, armature 68, and winding of magnet 24 to battery. Stepping magnet 24 energizes over this circuit and interrupts its own circuit to step the wi pers of the connector switch- Cfaround to normal position or until' the onfnormal springs 70 open, thereby opening the' circuit of magnet 24. As soon as the off-normal springs 70 open thelocking circuit of relay 16 is also opened and said relay 'deenergizes All of the apparatus in the finder connector link is now in nornal position and may be used for completing other calls.

It will now be assumed that the line of sub-V -station A is idle when the wipers of connector C are operated in engagement therewith. In this case the busy relay 21 will not be oper:

ated and when slow-acting .relay 19 deener- *gizes a circuit may be traced for energizing the switching relay 22 as follows: ground by way of the lower winding of switching. relay 22, armature 58, armature 45, resting` Contact of armature 51'and said armature, armature 29, test wiper 73, fourthbank Contact accessible to wiper 7 3, conduct-or 77, and through the lower winding of cut-ofi relay 84 to battery. Switching relay 22, upon energizing, at armatures 62 and 63 prepares a point in the ringing and talking circuit; at armature 64 grounds the fourth bank contacts en aged by wiper 73 in order to maire the line o substation A test busy to other switches; and for fully energizing cut-ofi` relay 84 atfiirmature 65 prepares a circuit for relay 21; at armature GG completes a locking circuit for itself from ground at armature 47 through its upper winding; at armatura 67 discon-V nects the'busy and dial tone leads; and at armature 68 opens a point in the circuit of stepping magnet 24 to prevent subsequent stepping of this magnet. The cut-off relay 84 is energized over the above circuit and at 90 armatures 85 and 87 disconnects itself and the common line relay LR from the line conductors 81 and 82. At armature 86a circuit is closed for grounding conductor 76 which terminates in the finder banks.

Since the calling subscriber A does not hear the busy tone he ,will dial ring the called subscriber A. In order to dial ring the called subscriber, subscriber A operates his calling` device in accordance with the dial ring digit which may be eithertlie digit'2 or the digit 8. In case the calling subscriber uses the digit 2 to dial ring the called line the bell of the called subscribers line would ring for only a short interval of time, while if the digit 0 was used the bell of the called line would ring for a predetermined longer period of time. In this manner it is shown that it is possible to have two parties 4on the same line and that they may be signalled by codes of either short or long ringing impulses. However, in this case since only one subscriber is shown assigned to a telephone line it is immaterial which .digit is used to dial ring the called line.v Responsive to the 115 operation of the calling device the line relay l is again intermittently operated and again causes the energization of slow-acting relay 19. The slow-acting relay, upon energizing, at armature 50 completes a circuit for busy relay 21 which is now used as a ringing re` lay. The circuit for energizing the relay 21 may be traced as follows: ground by way of armature 5.0, armature 55, working contact of armature 65 and said armature, and wind- ,12 ing or relay 21 to battery. Rela 21, upon en'- ergizmg, at armature 57 comp etes a circuit for ringing the called subscriber A as follows: from generator lead Gen. by way of the working contact of armature 57 ahnd said 13 armature, armature 53, armature 62, wiper 71, conductor 81, through the called line ringer and back to conductor 82, wiper 72, armature 63, andarmature 54 and its resting contact to ground. A short interval after the dialling impulses cease, slow acting relay 19 deenergizes and opens the circuit of relay 21 whereupon the latter relay also deenergizes. In case the called .subscriber does not immediately answer the calling subscriber may again dial ring the called line and again ring the bell of the called station. When the called subscriber A answers by removing his receiver during a non-ring pe-V riod or silent period a circuit may be traced for energizing relay 20 as follows: from ground byway of resting cont-act of a'rmature 54 and said armature, over the `previously traced circuit, lthis time, however. includingr the transmitter andvreceiver in bridge of the line and including armature 57 and its back contact through the lower winding of relay 20 to battery. Relay 20, upon energizing over the abovc-traced circuit, at armatures 53 and 54 completes the talking circuit; at armature 55 opens a point inthe circuit of relay 21 so that any further impulses will no t operate relay 21; `and at armature ,56 completes a locking circuit for itself extendingA by way of grounded armature 47. Calling subscriber A andcalled subscriber A are nowconnected and may talk over the talking conductors which are shown in heavy lines. Both subscribers receive their talking battery from the windings of line relay 17.

After conversation and when both subscribers replace their-receivers, relay 17 decnergizes and again causes the deenergization of sleeve relay 18. Relay 18upon .deenergizing, opens the-,locking circuit of relays 20 and 22 at armature. .47 and also closes at armature 49 the local circuit for returning the' connector switch wipers'to their normal positions. The release of the finder connector link is accomplished in the same manner a`s previously described. f All apparatus is novir in normal position a'nd is made 'available for other calls.v

Havingdescribed in detail themanner in which a, local connection is completed a detailed description of the operation that takes place when a local subscriber calls a subscriber in the main exchange will now be given. In making outgoin calls to the main exchange the local subscri er-must firstprex the digit 0 before dialling the regular telephone'- number of the main exchange subscribers line. e

For convenience, it will now be assumed that subscriberA desires yto complete a coll.-

nection with a mainJ exchange subscribersA line and responsive to the removal of the receiver at substation A the common line relay LR and cut-oil relay 4 operate 1n the same manner as previously described to cause a the inder F in Fig. 1 is the finder to be used.

and in case the Wipers of the finder are resting on the lin'e of substation A the der will immediately switch through in the same manner as previously described. Responsive to 'the subscriber AI dialling the digit 0 theJ connector C is directively operated in the same manner as previously described to set the Wipers on the tenth set of bank contacts. Now when relay 19 falls back shortly after the cessation of. impulses a circuit may be traced for energizing switching relay 22 and start relay 110 (Fig. 2) in series as follows: from ground by Way' of the lower windingV of switching relay 22, armature 58, armature-45, resting contact of armature 51 and said armature, armature 29, wiper 73, tenth bank contact. conductor 75, normally closed springs controlled by armature 188, in start conductor 178, arma-ture 154 and its resting contact, armature/135`and its resting Contact, and winding of start relay 110 to battery. Switching relay 22 energizes and operates its armatures in the same manner as previously described.

In the trunk circuit TC, Fig. 2, slow-t0- energize relay 110, upon energizing, at armature 136 closes a circuit for energizing diilerential relay 107; at armature 138 grounds night service control conductor 179 and prepares a temporary locking circuit for switch-through relay 109; and at armature 139 prepares a testing `circuit for stopping the trunk finder when the trunk finder finds the calling line and finder connector link. Diiferential relay 107, upon energizing, at armature 125 closes a self-interrupting circuit for the stepping magnet 105 .of the trunk finder TF. Responsive to the operation of Athe stepping magnet 105 the wipers of the trunkfinder are moved step-by-step in search of the calling finder connector link. When 'wiper 103 of the trunk finder TFencounters the bank contact in'which conductor 83 terininates a circuit may be traced including relay 14, wiper 11, conductor 83, fifthbank armature 60,.lower Winding of contact engaged by test wiper 103, armature"139, normally closed springs` controlled by armature 131,- lower winding of diierem' tial relay 107, fand through the winding of relay 108 to battery. Relay 107, being differentially adjusted, immediately releases its armature and stops the wipers of the trunk finder on the tengaged bank contacts or in this case on the Abank contacts in which the line of substation A terminates. Relay 108, upon energizing over the above-traced circuit, at armature 126 clos'esa circuit for energizing relay 109. Relay 109, upon ener- '4 gizing, .at armatures 127 and 128 completes a point in the talking circuit and also completes a circuit for energizing relay 111. At Aarmature 129 relay 109 opens the circuit through the upper winding of-diierential relay 107 at its back contact and at its front,

contact connects ground to conductor 89 to I maintain the' line of substation A busy to other switches which have access thereto. At

armature 130 relay 109 completes a locking circuit for itself, extending vfrom grounded armature 138; at armature 13,1 opens the circuit extending through the lower winding of differential relay 107 while maintaining thecircuit for relay 108; at armature 132 opens a point inthe circuit for stepping magnet 105; and at armature 135 opens the circuit of slow-acting start relay 110 at its resting contact-and at its working contact transfers the 'start lead to the next 'trunk circuit or to the common relay 186 in case thm-second trunk circuit is in use. The circuit for en.-.

ergizing relay 111.1nay be traced as follows:

from ground by Way of the normally closed springs controlled by .armature 146, armature 128, resting contact of armature 119 and said armature, wiper. 101, conductor 2, over the loop at substation A, conductor 1, wiper 100,

` ing slow-to-release relay 113; and at. arma-- ture 143 completes a locking circuit for re- "40 Ithe main exchange.

I relay 17; at armature 29 includes the' resistarmature 118 and its resting contact, armature 127, relay 111, conductor 170, and to battery at the main exchange. Relay 111, upon energizing over the above-traced circuit, at armature 140, completes a circuit for energizing release relay 112. Relay 112, upon energizing, at armature 141 opens a point in the circuits of relays 115 and' 116; at armature 142 completes a circuit for energizlay 109 before slow-acting rela'. 110 has had time to fall away. The circuit or energizing relay :113 may be. traced as follows: from Y ground at the main exchange, conductor 171, normally closed springs :controlled by armaance 32 in the circuit of rela 110; and at armature 31 completes a. loc g ci it for itself from grounded armature 40. 'ne relay 17, upon deenergizing, at the normally closed springs controlled by armaturev 42 short circuits the release relay 18, whereupon thev latter relay releases and opens the locking circuit of relay 22 and closes the local step-l e5 ping circuit for magnet v241er .returning the Wipers of the connector C to their normal positions as previously described. When the Wipers of the connector C are returned to their normal position the off-normal springs open the locking circuit of relay lpwhere.- upon relay 16 and then rrelay 14 deenergize to render the local finder connector link available for use on other calls. When lthe line ofp substation A is cu through to the main exchange by the' operation of relay 113, Fig. 2, the line switchindividual to this trunk line at the main exchange hunts for and connects With an idle first selector from which dial tone is transmitted back over the trunk line in the Well known manner. As vsoon as subscriber A hears the dial tone the subscriber will dial the main -exchange subscribers telephone number and the automatic switches .in the main exchange will respond thereto and complete the connec-` tion to the desired line. Talking battery is furnished from the connector inthe main exchange for both ,the P. A. X. subscriber and the ina-in exchange subscriber.

` After conversation and responsive to the main exchange subscriber replacing his rece1yer, the connector 1n themain exchange, being a release-by-last-party connector, 1s

prepared for release. When subscriber A rel, Y

lease relay 113 and at armature 143 opens the i circuit of relay 109. Relay 109, upon deenergizing, at armatures 127 and 128 opens points in the talking circuit; at'armature 129 removes ground from test Wiper 102 and conducto'r 89; at armature 132 prepares a circuit for magnet'105; and at armature 135 reestablishes the starting circuit for rela l110.

The trunk circuit TC and the trunk lin er TF arenow innormal position, it being understood however, that the wipers of the trunk finder TF remain in engagement with the bank contacts of the line last used and do not at this time return to their normal positions.

.The trunk inder TF and the trunk circuit TC may now be used for completing other connections.

'Having described the detailed operation which takes place. when there is an idle trunk finder and an idle trunk circuit, a description will nowbe given of the operation which takes 'place in case all of the trunk finders and trunk circuits are busy when ail attempt is made to extend a connection to the main exchange. It Iwill lnow beassumed that subscriber A attempts to make an outgoing call i'- when all the trunk circuits and trunk finders are busy. In this case the nder F and connector C are operated in the same manner as previously describedres onsive to the removal ofthe receiver andt e dialling of the in series when slow acting relay 19 deenergizes after the cessation of impulses. This circuit may be traced as follows: ground by way of the lower winding of switching relay 22, armature 58, armature 45, armature 51,

armature 29, wiper 73, conductor 75, normally closed springs controlled by armature 188, conductor 178, armature 154 and its resting contact and armature 135 and its working contact in case the trunk circuit is busy on an outgoing call to the main exchange or, by way of armature'154 and its working contact in case the trunk circuit is busy on an incoming call, outgoing start conductor 177, terminal 194, through the jumper 195 in dieating a chain circuit similar to armatures 154 and 135 in the second trunk circuit to terminal 193, and through the winding of relay 186 to battery. Relay 22 energizes in the same manner as previously described and at armature 64 connects directv ground to conductor 75 for, fully\operating,relay 186. Relay 186 is a slow-to-energize relay and when a circuit is closed through it in series with the 4lower winding of switching relay 22 relay 186 energizes only far enough to make the X contacts close at armature 190. Responsive to the closure of X contacts at armature y190 ground through resistance 191 is extended by way of the resting contact of armature 189 and saidarmature, over con`- ductor 167 to the tenth bank contact engaged by wiper 71 of connector Gand then by way of armature 62, armature 53 and its resting contact, armature 57 and' its resting Contact, and through the lower winding of relay 20 tobattery. Relay 20, upon energizing over the above-traced circuit, at armature 56 completes a locking circuit for itself by way of grounded armature 47; and at armature 53 prepa-res a circuit for transmitting the busy tone to the calling subscriber. When direct ground is connected to conductor 75 by the operatin of sleeveirela-y 22 relay 186 (Fig.

, 2) slowly pulls up its armature and at armature 188 completes a lockin circuit foritself and at armature 189 an its resting contact opens the original energizing circuit of relay 20 and connects busy tone over conductor 167 to wiper 71 at its working contact. The busy tone circuit may be traced from wiper 71 over the heavy talking con- 'p ductor to the calling loop and back to round vand t'o the lower winding of line re ay 17. Should any more7 local subscribers attempt to make an outgoing call at this time the connector C would operate in the same manner'as when a connection is completed to a busy local line because of the ground on conductor 75. Responsive to the receipt of the busy tone the calling subscriber replaces his receiver and therefore releases ,the finder connector linl inthe well known manner. When the wipers of the connector C are rotated off of the tenth set of bank contacts ground is removed from the conductor 'and rela-y 186 1s permitted to deenergize.

. Havingdescribed the detailed operation which takes place when a local subscriber calls a main exchange subscriber, the detailed description ofthe operation which takes lplace when a main exchange subscriber desires to be connected vwith a local P. A. X. subscriber will now be given. When the connector in the main exchange respons've to the main exchange subscriber dialli g the private automatic exchange number seizes a trunk line, say for instance, conductors'170 and 171, a circuit is completed for the A. C. relay 116 during the ringing period and for relay 'during the silent period. The cir-4 cuit for energizing A'.' C. relay 116 is closed from the generator at the connector over conductor 170, armature 141, winding of relay 116, armature 157, and condenser C3 to conductor 171. Relay 115 is bridged across the trunk conductors in series with resistances 155 and 156 and operates when the trunk is seized. Due to fthe inclusion of the rsistances 155 and 156 the ring-cut-off relay in the main exchange connector is not voperated at this time. Responsive to the operation of relay 116 said relay at armature 159 closes a locking circuit for its lowerwinding extending from'grounded conductor 180 by way ofarmature at armature 157 opens its original energizing circuit; and at armature 158( closes. a circuit for lighting the answering lamp 203 as follows: from grounded spring 206- of release key RK, conductor 180, armature 158,'conductor 181, answer lamp 203, conductor 261, restin contact of spring 213 and said spring, and t rou h the windingof relay 207 to battery. Re ay 207 energizes over the `above-traced circuit and at 'armature 208 completes-a circuit for operating the buz-.

.zer relay 222 as follows: ground bywaypof spring 219 and its resting contact, conductor 275 which is looped through springs similar to the spring assembly 219 in the answer key individual to the second trunkcircuit, ter- Aminal 292, jumper 291, designating the chain circuit through the various trunk keys, terminal 293, conductor 268, interrupter spring 223 of the buzzer 222, windin bf buzzer 222, and armature 208 to battery. elay 115, upon energizing over the above-traced circuit, at

armature 156 closes a circuit for energizing relay 114.-., Relay 114; upon energizing, at armature 149 completes a new bridge across the trunk circuit independent of armaturey 141; at armature 150 closes a circuit for energizing relay 113; at armature 151 opens the short circuit around the lower winding of relay,112;4 at armature 152 prepares a locking circuit for relay 109; at armature 153 izanv prepares an energizing circuit for relay 117 and at armature 154 switches the trunk finder start lead 178 to tlie next. trunk finder or to the common relay 186. Relay113, upon energizing, at armature I146 connects' upkthe lower talking conductor and at armature 147 prepares a locking circuit for itself.

When the attendant hears the'buzzer sig-I nal and observes the lighted condition of the answer lamp 203 she will first remove her monophone from its cradle, thereby operating the crade springs 201 and l 202 and then operate the answer key AK associated with the trunk c'ircuit TC. The closure of the cradle springs 202 closes a circuit for energzing line relay`230 asfollows: ground by way of the lower winding of relay 230, conductor 270, resting springof spring 280 and said spring, conductor 278, impulse springs of the calling device CD,`transmtter, re-

ceive'r,4 spring assembly 202, conductor 279,`

spring 281 and its resting contact, conduc-v tor 271, and through the upper winding of 'relay 230 to battery. Relay 230, upon energizing, at armature 253 opens 'a normally closed short circuit from around release relay 228 and also closes an energizing circuit for relay 228 which may be traced as follows: ground by way of armature 253, winding of release relay 228, normally closed springs controlled by armature 234, conductor 175, armature 124, and winding of magnet 105 to battery. The latter circuit is not completed at this time because relay 106 is not at this time energized. Responsive to the operation of the answer key AK spring assembly 216 lease kezy substitutes ground at the monophone spring 201 for the ground. at springs 2:05 'of the re- RK; spring assembly 217 lead 26 and theans'wer control lea 173 in order to energize relay 117 in the trunk circuit TC; at spring assembly 218 connects conductors 260 and 261 together independent of the night key NK; at spring assembly 219V opens the buzzer circuit 'at the back contact and at its working contact closes a circuit for energizing slow relay 229; and -at sprin asg conductors 184 and 185 to talking conductorsV 272 and 273, Y Thecircuitiorenergizing relay Y -117 may be gtraceda's follows: -from ground by way of the working contact ofspring 201,

working contact of spring-217 end said spring. conductor 267, armature231yanswer.

control conductor v173, armature 153, and through the lower winding of relay 117 toV battery.` Relay 117, upon energizing, 1at armature 160 connects thetalking conductor 184 to conductor 171 and also closes a shunt circuit around the resistanees 155 andl 156 in order to operate the ring-cut-o relay in the connector in order to cut oi the ring;` at.v armature 161 closes a holding circuit for relay 114 independent 'of armature 156; at

armature 162 templates a self-interruptingA ounds A circuit for magnet 105 in order to return the trunk finder TF to its normal or home position; at armature 163complctes a locking circuit for itself through its upper windin to 'grounded disconnect conductor 180; an at armature 165 prepares a circuit for lightin .the supervisory lamp 204; -A. short interva a circuit for locking relays 224 and 225 and at armatures 251 and 252 closes the talking circuit to the attendants substation.

The circuit for returning the trunk finder TF to its home position may be traced as follows: from grounded answer control conductor 17 3, armature 162, armature 144, armature 123, armature 132, ofi-normal springs A 104, interrupter springs of magnet 105, and 4 through the magnet to battery. Magnet 105 intermittentl operates over the abovetraced circuit an returns its wipers to' home 1 position at which time the off-normal springs 104 willy open. It will be noted that the upper winding of relay 106 isnormally short Vcircuited as long as the off-normal springs 104 remain closed but as soon as the off-normal springs 104 o en, a circuit may be traced csf from grounde answer control 'conductor 173 over a portion of the previously traced circuit to armature 123 from whence it extends to the upper winding of relay, 106 and through the interrupter springs of magnet 105 and winding of vmagnet 105 to battery. Relay 106 is energized over this circuit but due to the high resistance of relay 106.step

ping magnet 105 is not energized. Rela 106 at armatures 11,8 and 119 pre aresaI ciicuit for ringing thev called subscri r; at arma-v tureg120 connectsthe common test conductor 17 6to wiper 1 02; at armature 121 completes a locking circuit for itself to grounded an- ,swer control conductor 173; at armature 122 prepares acircuit for switch-through relay` 109; at armature 123 o ns -a polnt 1n the circuit for its u per win ing as well as opening the circuit or returning the trunk finder com letes the circuit for the release rela 228 1n the comm-onl trunk relay grouY as we repares the impulse circult for t e trunk. i

H5 to its home position; and at armature 12A gizing, at armature 245 prepares the 1m' pulsing circuit over common pulse armature 247 prepares a locking circuit for relays 224 and 225.

Theattendant now asks the main exchange condnctor |25 175 at armature 246 prepares a testing circuit' which includes switching relay 225; and atl subscriber for the number of 'the desired local subscribers line. Assunung that -subscriber A is the desired subscriber, the atattendants calling device.

tendant. will therefore operate her calling device CD iu accordance with the number of tho line of substation A. In this case the line number ot'4 substation A is 5 and accordingly five impulses are transmitted from the lVhen the attendants calling device CD is moved off-normal the shunt spring assembly 283 4closes and shunts the transmitter and receiver thereby closing a direct circuit for liuc relay 230 and during the return to normal the impulse spring 277 interrupts the circuit ot' relay 230 five times; Responsive to each interruption in its circuit relayT 230 energizcs a corresponding number of times and for each deenergization relay 230 transmits a ground impulse for operating magnet 105 as follows: ground by way of armature 242, armature 245, normally closed springs controlled by armature 253, normally closed springs controlled'by armature 234, common pulse conductor 175, armature 124, and winding of magnet 105 to battery. By the operation of the magnet 105 the trunk finder wipers are operated step-bystep to the line of substation A. Each time line relay 230 deenergzes said relay at the normally closed springs controlled by armature 253 closes a short circuit around relaV 228 so 'as to render this' relay slow to release during impulsing` and at armature 264 transmits an impulse of current for energizing slow-to-release relay 227; At armature 243 relay 227 prepares a circuit for operating combined busy and ringing relay 226; at armature 244 maintains ground on the impulsing circuit independent of armature 242 in case relay 226 is operated while wiper 102 is passing over grounded contacts; and at armatures 248 and 249 opens the talking conductors extending to the trunk conductors 170 and 171 in order to prevent the main exchange subscriber hearing the dialling impulses.

Further operation now depends upon whether the line of substation A is busy vor idle. If the line of substation A is busy ground on conductor 89 'engaged by test wiper 102 causes relay 226 to energize over the following circuitzfrom grounded conductor 89 by'way of testwiper 102, working contact of armature 120 and said armature, common test conductor 17 6` armature 243 and its-working contact-,and through the Winding of relay 226 to ibattery. Relay 226 at armature 239 opens a lpoint in the circuit of 'cut-olf relay 224; at armature opens a point in the circuit of `the switching relay- 225; at armature 2,42 removes groundfrom the impulsing circuit; and at armature 241 closesl a locking circuit for itself including grounded test conductor 176 and armature 237. After a short interval of time,slow

.acting relay 227 deenergizes and at armature 243 and its resting contact prepares a point* yline A is busy and if Ythe main exchange subscriber Wants to Wait she may do so. Now when the called line becomes idle ground vis removed from conductor 80 and test wiper 102, tl1ereby causing the deenergization of relay 226. Relay 226 at armature`241 completes a circuit for energizing switching relay 225 and at armature 242 again applies ground for the impulsing circuit. The circuit for energizing switching relay 225 may be traced as follows: ground by way of armature 246, upper winding of relay 225, armature 240, resting contact of armature 43 and said armature, conductor 176, armature 120` testwiper 102, conductor 89, and through the lower winding of cut-otf relay 4 andl resistance R to battery. Switching relay 225, up-

on energizing, at ar1nature234 disconnects conductor17 5 fromrelay 228 and substitutes the battery through resistancer233 for the ing circuit and a circuit for the ring-cut-of relay 224; at armature 237 -connects ground to conductor 176 in order to make the called line test busy and fully operate the cut-off relay 4; and at armature 238 locks up through its lower winding to ground at armature 250.

In the trunk circuit TG, Fig. 2 switching relay 109 is energized over the following circuit: from ground at armature 235, common switch through conductor 174, armature 122, and winding of switch-through relay 109 to battery.` Relay 109, upon energizing, at armatures 127 and 128 prepares a point in the talking circuit; at armature 129 prepares a point in the circuit for grounding test wiper- 102 after relay 106 falls back;,at armature 130 locks up to grounded local release conductor 183; at armature 132 opens a point in y the restoring circuit of magnet 105; at armature 133 prepares a ground return circuit for ringing the called line; at armature 134 completes a: circuit for lighting the supervisory lamp 204; and at armature 135 opens a further point in the circuit of start relay 110. The circuit for lighting the supervisory lamp 204 may be traced as follows: from' ground by way of disconnect conductor 180, armature 45, armature 134, armature 165, supervisory lead 182, supervisory lamp 204, conductor 261, spring assembly 213, and Winding of relay 207 to battery. By vthe lighting of the supervisory lamp formed that the called line is now idle and accordingly dial'rings the vcalled line. Responsiveto the operation of the calling device CD, line relay 230 is againintermittent- 204 the attendant is in-.

.following circuit: ground by way 01K the working Contact of armature 237 and said armature, armature 243 and its working contact and winding of relay 226 to battery. At armature 239 relay 226 connects generator GEN to the called line over the following circuit: from generator GEN, working Contact of armature 239 and said armature, armature 236, common ringing conductor 172, working contact ot armature 118'and said armature, wiper 100, conductor 1, through the substation ringer and condenser of line A, conductor 2, wiper 101, armature 119 and its working contact, working contact of armature 133 and said armature, to grounded disconnect conductor 180. Shortly after tliedial ring impulses cease, slow-acting relay 227 deenergizes and opens the circuit of relay 226- which accordingly deenergizes. Relay 226, upon deenergizing, at armature 239 prepares a circuit for energizing ring-cut-oi re' lay 224 when the ycalled line answers. If the called line does not immediately answer the attendant can dial ring again and ring as -many times as needed. When subscriber A answers during a silent period a direct current bridge is substituted for the condenser and ringer and accordingly the ring-cutoif relay 224 is energized over its upper windi ing and over the ringing circuit as previously traced to grounded disconnect conductor 180.V Relay 224, upon energizing, at armature 231 opens .the circuit of relay 106 and at armature ,232 closes a locking circuit through its lower winding to grounded armature 250. Relay 106 upon deenergizing, at the working contacts of armatures 118 and 119 opens the ringing cirbuit and at the back contacts thereof completes the talking circuit and completes an energizing circuit for relay 111; and at armature 120 connects grounded 'armature 129 to test wiper 102. The circuit orenergizing relay 111 may be traced as follows: ground at the main exchange, conductor 171, armature 146 and its working contact, armature '128, resting contact of armature 119 and said armature, wiper 101, conductor 2 through the receiver and transmitter at the called station A, conduct-or 1, wiper 100, armature 118 and its' resting I Contact, armature 127, winding vof relay 111,

conductor 170, to battery in the main exchange. This battery and round connection at the main exchange is tirnished through windings of the soscalled back-bridge relay in the connector switch. At armature 140 relay 1 11 closes a circuit for energizing relay 112 through both its windings in series. At armature 145 relay 112 opens the locking circuit of relay 116 and' also opens the circuit o fthe supervisory lamp 204, Relay 116, upo deenergizing, atarmature` 158 opens the circuit -operated another trunk key.

Maaate of the answering lamp 204 and also causes relay 207 to deenergize.

The operation which takes place in case the line is idle when initially called is the same as just described, with the exception that in such ,case busy relay 226 is not ,energized from the busy line and the supervisory lamp 204 is thus responsive to the operation of switch-through relay 109 which informs the Y' attendant that the line is idle. rlhe operation from here on is the same as previously described.

After the called subscriber answers the at- .springs 219 the circuit of slow-acting relay -229 is opened whereupon said relay releases and at springs 220 and 221 theftalking circuit to the attendant is opened.` At spring 219 the 'circuit for buzzer 222 is again closed in case the attendant has not in the meantime Relay 229, upon deener 'zing, at armature 250, opens the locking circuit of relays 224 and 225 and at armatures 251 and 252 opens a further point in the talking circuit to the attendants telephone set. Responsive to the placing of the monophone on the cradle springs 201 and 202 are loperated and springs 202 open the circuit of line relay 230 in the common trunk relay group. Line relay 230, upon releasing, opens and short circuits relay 228 which thereupon deenergizes. Relay 227 is momentarily operated at this time without any effect. The attendants equipment and the relays in the common trunk relay group are now in normal position and may be used on other calls.

y llhennain exchange subscriber and subscriber A may now converse as desired, the talking battery being furnished lfrom the main exchange.

During the time the main exchange subsc'riberY is connected with subscriber A the main exchange subscribermay inform sub-.-

at intervals. When subscriber A depresses 1 thei'switchhook thereatthe circuit for relay 111 is opened and therefore said relay deenergizes. Relay 111 opens the circuit of relay 112`which thereby deenergizes and at armature 145 closes a circuit for operating the supervisory lamp 204 and relay 207 to operate the buzzer as previously described. By the intermittent operation of the switchhook at substation A relays 111 and. 112 are intermittently operated to flash the supervisory lam 204 tocall t e attention of such a call tot e attendant. hen the attendant notes the iashing of supervisory lamp 204 she will again remove the monophone from the cradle and again operate the answer key AK. Re-

sponsive to the removal ofthe monophonefrom its cradle the line and release relays 230 and 228, respectively, are operated. By the operation of the answer ke relay 229 is again energizedand thev atten ant is again connected across the trunk. The main exchange subscriber or subscriber A informs the attendant that the main exchange subscriber wishes to converse with subscriber A after which the subscriber A replaces his receiver on the switchhook. The attendant momentarily depresses the monophone .cradle springs, thereby separating springs 201 and 02 from their switching contacts. With the answer'key AK in operated position and the operation of springs 201 and 202 s rings 201 therefore removes ground from t e locking conductor 183, thereby causing relay 109 to ileenergize. Relay 109,l` upon deenergizing, at armature 127 opens the ycircuit of relay 111; at armatures 127 and128 opens a point in the talkin circuit; at armature 129 removes grou'n from wiper 102.; at armature 132 short circuits the upper winding of'relay 106 and prepares the self-interrupting `circuit for magnet 105; at ,armature 133 closes a circuit for energizing relay 116; and at armature 134 opens a point in the circuit extending to the supervisory lamp 204. Relays 1'11 and I 112 accordingly deenergize.

as follows: from ground by way of grounded disconnect conductor 180, armature 133 and its resting contact, armature 164 and through the lower winding of relay 116 to battery. Relay 116 at armature 158 closes a circuit for lighting the answer lam 203. i Responsive to the lig ting ofthe answe lamp 203 the attendant releases the cradle springs causing springs 201 and 202 to er1- gage their worklng contacts. At springs 201 the circuit is completed for stepping magoperation from now on will be the same asv explained for the connections completedto substationA. f y

After conversation and in case the main exchange subscriber replaces his receiver first, all of the switches except the connector in the main exchange release. The main exrIhe circuit for energizing relay 116 may be traced .plainly seen that if during the processl of change connector is of the well known releaselsubscriber hangs up his receiver. i When the subscriber A or A, as the case may be, rev places his receiver, thecircuit of relay 111 is,

Opened and said relay accordingly deenergizes. At armature 140 relay 111 opens the circuit of relay 112 and said relay deenergizes and operates the supervisory lamp 204 and l'I5 buzzer sincev in the meantime the attendant has released the key AK. Responsive to this signal the attendant throws the release key RK, thereby removing ground from 'conductors 180 and 183, causing the deenergization of relay 109 and 117. Relay 109, upon deenergizing, at armature 129 removes ground from test wiper 102 and conductor 77. Relay 117 is made slow acting so as to insure therelease of relay 109 before relay 117 can release and connect ground to its resting convtact at armature 116. Relay 117, upondeenergizing, at arma-ture 116 removes the short circuit around-the resistances 105 and 106, thereby causing the back-bridge relay in the main exchange connector to return tonormal position. The main exchange connector accordingly releases in case the main exchange subscriber has replaced his receiver and by this release the connector opens the circuit of relay 115 which also deenergizes. At armature 156 relay 115 opens the circuit of. slow-acting relay 114.` Relay 114 deenergites and opens the circuit of relay 113 at armature 150. When relay 113 returns to its normal position the trunk finder and trunk circuit is made available for. use on other calls. In case the P. A. X. subscriber releases first, relays 111 and 112 deenergize thereby operating the supervisory lamp 204 and the buzzer 222. The attendant now operates the release key RK and releases the local connection as .previously described. The back bridge relay in the connector is alsol deenergized and as soon as the main exchange subscriber replaces his receiver .all the switches in the main exchangeA will release in the well known manner.`

From the foregoing description it can bev aoy setting up one call another call comes in, the attendantmay release from the first call. and v attend to the second call by restoring the answer key of this trunk and operating the answer key of the other trunk. After complet.- ingfthe second call the attendant may return to the first call and then-complete such desired connection.

' Having, described local incoming and outgoing calls a description of the o eration which takes place will now be given 1n which the P. A. X. subscriber calls the attendants f n relay at armature 64 connects dlrect groundV noted, is given a local telephone number ing the wipers of the connector C to engage the ninth set of bank contacts in which the conductors 90, 91 and 93 terminate. Switching relay 22 energizes over the following circuit from ground by vvay of the lower Winding relay 22, armature 58, armature 45, resting contact of armature 51 and said armature, armature 29, wiper 73, ninth bank contact, conductor 93, and through the left hand Winding of attendant-s cut-off relay 97 to battery. lVhen switching relay 22 energizes said to the attendants cut-off relay, thereby causing thefull operation of said cut-ofil relay. Subscriber A nowdial rings the attendant, thereby causing the operation of the ringer 282 at the attendants substation. The ringing circuit extends from generator GEN at armature 57 over the wiper 71, conductor 91, through the ringer 282, conductor 90, wiper 72 to ground at armature 54. Responsive to the operation of the ringer 282 the attendant operates the line keyfLK, thereby directly connecting her substation with conductors 90 and 91 as soon as she removes the monophone ,from its cradle. As soon as the attendant removes the monophone from its cradle, a direct current bridge is closed across conductors 90 and 91 whereupon the relay 20 in the connector C energizes and completes the talking circuit. Both the attendant and subscriber A receive their talking current from relay 17. The attendant can disconnect from the circuit of the trunk by the restoration of the keyLK in order to answer and supervise incoming trunk calls and then return to the local connection by merely operating the key LK. After conversation the release of the connection is the same as previously described.

The attendant can also initiate a call using the local finder connector links by removing the monophone from its cradle and by operating the line key LK. This operation causes the common line relay LR to operate and start an idle finder connector link to hunt for the attendants line. The attendants cutolf relay 97 is operated in its first step in series with the common line relay LR and is operated in its second step when the finder F 'inds the attendants ,K line. The attendant then operates the calling device in accord-` ance withthe number of the desired called line and the connector C is operated to comiyzeafisq.

Since in a system of this size the attendinstructions a certain specified local subscribers line may always be designated for night service and the attendant would therefore prepare such line for night service before leaving her position. Before the attendant leaves her position she will remove her monophone and operate the answer key associated with the trunk to be used for night service and listen in on the trunk to determine if the trunk -is busy. If the trunk is idle the attendant operates the night key NK in order to seizeI the trunk. Responsive to the operation of the answer key AK relays 228, 229, and 230 energize as previously described and responsive to the operation of the night key NK a circuit is closed for energizing relay 115 and for grounding the night service control conductor 179. The circuit for energizing relay 115 may be traced as follows.:

'ground by way of'resistances 209 and 210,

Working Contact of spring 211 and said spring, spring 220 and its working contact, conductor 1811,- winding of relay 115, armature 141, conductor 170, to battery through the line relay of the line switch atthey main exchange. Thegline relay at the main exchange does not energize over the above traced circuit onaccount of the high resistance of resistances 209 and 210 and relay 115. Relay 115, however, energizes over the abovetraced circuit and at armature 156 again causes the operation of relay 114. Relay 114 again causes the operation of relay 113 and at armature 153 closes a circuit for energizing relay 117 which may be traced as follows: from grounded cradle springs 201, springs 217, conductor 267, armature 231, conductor 172, armature 153, and to the lower winding of relay 117 to battery. Relay 11.7 at ari ture 162 again closes the circuit for restoring the trunk finder to its normal position and at armature 164 closes a circuit for energizing relay 116 by wa of grounded disconnect conductor 180 an armature 133 as previously traced. At armature 158 rela 116 closes a circuit for lighting the answer .lamp 203 in the same manner as previously described. After the trunk finder is returned to its normal position'relay 106 is energized in the same manner as previously described after which the attendant dials the number of the arty to be connected up fernight service. Iln case the line is idle, switching relay 225 is energized when the trunk finder wiper seizes the line of the called subscriber and closes the circuit for energizing the switch-through relay 109 in the trunk finder. Switch-through relay 109 accordingly energizes and locks itself lamp 204. By the lighting of the supervisory lamp the attendant knows that the line of substation A is now prepared for night service and since no means is provided for the attendant to talk'to such a line set up for ni ht service the attendant can code ring such sul scriber in such a manner as to inform the restores the answer key AK and replaces the monophone 011 its cradle. The common control relays CTR are restored to then-normal position 1n the same manner as previously described and relay106 in the trunk finder also deenergizes and completes a direct circuit from the line of substation A direct through to the main exchange. VRelay 106, upon deenergizing., at armature 120 connects direct ground at armature 129 to test wiper 102 so as to make the line set up for snight service busy to other locallines. Inthis mannerfit can be seen that the line set up for night service can be called from the main exchange and make main exchange calls but cannot complete any local connections. Responsive to the restoration of the answer key AK to its normal position the circuit of the answering and supervisory lamps 203 and 204 are opened and accordingly' the lamps are extinguished,

The subscriber rA can now receive and make main exchange calls. In order to make a main exchange call subscriber A merely removes his receiver and listens for the dial tone from the main exchange and after receipt thereof dials the main exchange subscribers telephone number without preixing the digit O because his line is now in direct' connection -with the main exchange. The operation of the switches in the .main exchange is well' understood'and need not be explained. M

Calls to subscriber A in the main exchange are completed tothe line of substationAover conductors 170 and 171 in the ordinary man'-l ner since this station is now connected up the same' asany other main exchange subscriber'. It is possible for other local subscribers to make outgoing calls to the main exchange bverthe other trunk circuit (not shown)l but no incoming p this trunk circuit because the attendant-has left her position.

Having described the-invention, what isv considered new and is desired to have ro# t-ected by Letters Patent will be set fort in calls can `be completed overv operating said 1 and for then directively operatin said findhome position but'l normally remaining in line for causing said finder to find the calling line, and means for automatically returning said inder to its home position re-J sponsive to the act of answering an incoming call over said trunk line.

2. In a telephone system, a trunk line, a finder individual to said trunk line having a home position but `normally remaining in the position last used, meansi responsive to the initiation of an outgoing call over said trunk line for causing said finder to iind the callin line, means for automatically returning saigd finder to its home position responsive to the act of answering an'incolning c all over said trunk line, and means effective thereafter for directively operating said finder to extend the incoming call to a called line.

3. In attrunk finderA having a home position but normally remaining in the position last used, a stepping magnet, a circuit for automatically operatin said magnet to cause the wipers of the fin er to find a calling line, a second circuit for automatically operating said magnet to return the wipers to their home position, and a third circuit for directively operating said magnet to move the wipers into engagement with a called line.

4c. In a two-way trunk line terminating in one end in a trunk finder, the wipers of said trunk finder having a lhome position but to find a calling line on outgoing calls, means for automatically advancing the wipers of said finder to home position under predetermined conditions, and means for thereafter directively operating said inder to connect with a called line on incoming calls.

5. In a combination finder and connector switch of the type in which the wipers move in a forward direction only, means for operating the switch as a finder on successive calls without restoring the wipers, and means for restoring the wipers when the-switch is used as a connector.

6. In a telephone system, subscribers lines a two way trunk, a finder switch individual to said .trunk having access to said lines, said finderhaving. a homeposition but'normally remaining in the position last used, meansr including'a stepping magnet for operating,

said` finder to connect a line with said trunk when theline is calling, and means including said Steppin magnetfor automatically nder to its homeposition er to complete a connection to sai line when the line is called.

7. In a telephone system, a trunk line,a

finder individual to said trunk line, said i lnder having a home pqsition but normally remaining in the position last used, means responsive to the initiation of an outgoing call for causing said linder to find and connect With the calling line, an attendants cabinet, an answer key individual to said trunk line at said cabinet, and means responsive to the operation of said key when the at tendant answers an incoming call over said trunk line for automatically causing said finder to return to its home position.

8. In a telephone system, a trunk line, a linder individual to said trunk line, said finder having a. home position but normally remaining in the position last used, means responsive to the initiation of an outgoing call for causing said finder to find and' con.- nect with the calling line, an attendants cabinet, au answer key individual to said trunk line at said cabinet` means responsive to the operation of said key when the attendant answers an incoming call over said trunk line for automatically causing said finder to return to its home position, and means efi'ective thereafter controlled by the attendant for directively operating said finder to com plete a connection with a called line.

9. In a telephone system, a trunk line, 'a finder individual to said trunk line, said finder having a home position butnormally remaining in the position last used, lmeans responsive to the. initiation of an outgoing call for causing said finder to find and connect with the calling line, an attendants cabinet, an answer key indivi-dual to said trunk line at said cabinet, means responsive to the operation of said key when the attendant answers an -incoming'call over said trunk line for automatically causing said finder to return to its home "position, means effective thereafter controlled by the attendant for directively operating said finder to complete a connection with a called line, and means responsive to further impulses generated by I the attendant for dial ringing the said calle-d line. l

10. In a telephone system, subscribers lines, a link circuit including a finder switch and a connector switch, means responsive to the initiation of a call by a calling subscriber for operating said finder to connect said link circuit to the calling line, means for directively operating said connector to extend the connection to a called line, a combined lbusy and ringing relay in said connectorz a -busy tone source., means for operating sald relay to connect the busy tone to the calling line in case the called line is busy, means orpreventing` the connection of said bu'syton'e to the calling line ip case the called yline 1s idle, a source of ringing current, and means for thereafter operating said relay to connect said ringing current to the called line.

11. In a telephone system, a branch exchange and a main exchange, subscr1bers lines terminating in the branch, means in the branch for completing local connections -it to said truuk line via said switch, means then effective for making said line busy to all other local lines, and means whereby said line can call only main exchange subscribers or can only be called by main exchange subscribers.

l2. In a telephone system, subscribers lines, a link circuit comprising a finder switch and a connector switch, means responsive to the initiation of a call by a calling suh- -scriber forcausing said finder to find the calling line, means responsive to directive control from said calling line for causing said connector to extend a connection to a called line, and means in the connector responsive to directive control from ythe calling line for diall ringing the called linea Y 13. In a telephone system, subscribers lines, a link 'circuit comprising a finder and a connector switch both having access to said lines, means responsive to the initiation of a call for causing said finder to find the calling line, means responsive to impulses generated by the calling subscriber for operating said'connector to extend a connection to a called line, and means in the connector' responsive to further impulses generated by Ithe calling subscriber for signalling the called subscriber in accordance therewith Whilesaid impulses are being received.

14. In a telephone system, subscribers lines, a link circuit comprising a finder and a connector switch botlrhaving access to said lines, means responsive to the initiation of a call for causing said finder to find the calling line', means for transmitting a distinctive tone to the calling line as soon as the finder lindsthevcalling line, means responsive to impulses generated by the. calling subscriber for operating said connector to extend a connection to a called line, and means in the connector responsive to further impulses generated by the calling subscriber for signalling the called subscriber in accordance therewith coincident With the receipt of such impulses.

l5. In a telephone system, a main exchange and a branch exchange, a plurality of two-way trunk lines interconnecting the exchanges, a trunk finder individual to each trunk line at the branch exchange, means for automatically operating said finders to find calling branch exchange subscribers lines responsive to the initiation of outgoing calls from the branchexchange, and a group of relays common to 'said trunk lines for directively controlling said'trunk finders to connect with called branch exchange subscribers lines on incoming calls from the main exchange.

16. In a telephone system, a main exchange and a'branch exchange, a plurality of two-way trunk lines interconnecting the exchanges, a trunk linder individual to each trunk line at the branch exchange, means for automatically operating said finders to find calling branch exchange subscribers lines-responsive to the initiation' of outgoing calls from the branch exchange, a group of relays common to said trunk lines, and means in said group for cau-sing said iinde'rs to be directively operated to called branch exchange subscribers lines, for causing said finders to seize and make busy the called lines, for ringing the called lines', for cutting 0E the ring when the called lines answer, and for causing said inders to switch through and connect the called lines to the trunk lines on incoming calls from the main exchange.

17. In a telephone system, a two-way trunk line, a switch terminating said trunk line, means for operating said switch as a hunting finder to connect a calling line with said trunk line, operators equipment for transmitting impulses to said switch to opcrate the switch as a connector to connect the trunk line with a called line, and a circuit excluding the trunk line over which said impulses are, transmitted.

18. In a telephone system, a trunk line connecting a branch exchange with aimain exchange, a `switch terminating said trunk' line in the branch exchange, means for operating said switch as a finder in a branch to main exchange call, and attendants equipment including a calling device in the branch exchange for directively operating the switch as a connector in themain to branch exchange call. 'l

19. In a telephone system, a. directively controlled connector switch for setting up` connectionsto called lines, -said switch normally standing in the position last used, and means including the stepping magnet of the switch for automatically advancing the switch to home position responsive' toits being taken into use for a new call. n

20. In a telephone system, a trunk hne terminating in an automatic switch, saidV switch -standing normally in the positlon last used, a branch of said trunk .extending to an operators position, means for signalling the operator when a call is received, and means for restoring said switch to home position responsive to the answering of the call by the operator.

21. In a telephone system, a trunk line extending rom avmain exchange to a branch exchange, a switch terminating said trunk line at the branchiexchange, said switch standing normally in the position last used, operators equipment at the branch exchange for hantivelyvoperate said switch into engagement with a called line, a relay in said switch operative responsiveto subsequent impulses from said calling device for projecting ring- -ing current out on the called` line during each series of impulses, and a talking circuit including said trunk line and said switch in set position but excluding the branch extending to the operators position.

23. In a telephone system, a main exchange and a branch exchange, trunks connecting said exchanges and terminating in switches at the branch exchange, subscribers lines terminating in the branch exchange, an attendant at the branch exchange, subscriber controlled means for operating the switch of an idle trunk to connect the trunk with a *calling line, means controlled by the at. tendant for operating the switch of a trunk over which a call has been extended from the main exchangeto further extend the connection to a wanted subscribers line, and means controlled by the attendant for operating the switch of an idle trunk to connect with an idle line, whereon calls originating on said line will be extended directly to the main exchange and calls originating at the main exchange will be extended directly to said line.

24. In a telephone system, a main exchange and a branch exchange, a trunk line connectkmeans for operating said switch to set up a connection from a calling line to the main exchange via the trunk line, means for operating the switch to set up a connection from the main exchange to a wanted line, means `for opening the connection at the termlnation of a call, means for operating said switch to set up a connection from the trunk line to a subscribers line for night service calls from either exchange to the "other, and means for preventing the opening of the night service connection at the termination of' such calls. v 25. In a telephone` system, trunk lines connecting a main exchange and a branch exchange, a switch terminating each trunk line, means for operating said switches as finders in branch to main exchange calls, and common control means for operating'said switches as connectors in main to'branch exchange calls. .A

26: In a telephone system, trunk lines connectlng a main exchange and a branch exchange, a switch terminating each trunk line,

' means for operating said switches to connect with calling lines in branch to main-exchange calls, and a common controlcircuit for dinrectively operating said switches to connect wiltlh wanted lines in main to branch exchange ca s.

27. In a telephone system, trunk lines connecting a main exchange and a branch exchange, a switch terminating each trunk line,

means for automatically operating theswitch l associated with an idle trunk to extend a connection from a calling line to the main exchange, and means for-transmitting directive 15 impulses to a switch independent of the associated trunk line to extend a connection f from the main exchange to a wanted line in the branch exchange. l

28. In a tele hone system, subscribers 2 lines, a link circuit comprising a'inder switch and a connector switch, means responsive to the initiation of a call for operating said finder to hunt for and connect with the calling line, means responsive to directive digits transmitted over the calling linefor operating the connector to extend a connection to a called line, a source of alternating current, and means in the connector responsive to y directive digits transmitted over the calling line for connecting said 'current source to the 1 'called line during the transmission of each difrit. l

n witnesswhereof, l hereunto subscribe my name this 21st day of December, A. D.,

Joran iii. Voss.l

to r 

